F12 - Why is root having 2x better performance when running glxgears than "normal" user?

[jaivuk]

Hi guys,

I'm running kernel 2.6.31.12-174.2.19.fc12.i686 on Acer Aspire One.
For the purpose of this test I disabled cpuscaling so CPU is running at the
full speed 1600Mhz:

When I'm running glxgears as normal user I get this stats:
526 frames in 5.0 seconds = 105.186 FPS
547 frames in 5.0 seconds = 109.283 FPS
565 frames in 5.0 seconds = 112.826 FPS
521 frames in 5.0 seconds = 104.118 FPS
562 frames in 5.0 seconds = 112.389 FPS
558 frames in 5.0 seconds = 111.434 FPS

However when I'm running it as root I get:
1229 frames in 5.0 seconds = 245.583 FPS
1220 frames in 5.0 seconds = 243.777 FPS
1228 frames in 5.0 seconds = 245.375 FPS
1225 frames in 5.0 seconds = 244.774 FPS
1182 frames in 5.0 seconds = 236.090 FPS
1200 frames in 5.0 seconds = 239.892 FPS

I would expect some difference but not as huge (more than 2x).
Latencytop shows that glxgear spends most of the time on "Scheduler: waiting
for cpu" in both scenarios.

I also tested gtkperf and I did not see the same behaviour - root was less
than a second faster in overall test but normal user was faster
in GtkDrawing tests.

Do you have any explanation for glxgears results?

Thank you,

Jaiv
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